For these analyses, methods such as western blots, immunofluorescence, growth curve, sequencing of the passaged viruses were applied. Antigens The SIVgag was kindly provided by M. inhibitory. In a prime-boost regimen, in the presence of MV-nAb, the intranasal-intramuscular (i.n.-i.m.) or Promazine hydrochloride intramuscular-intramuscular (i.m.-i.m.) routes induced higher humoral immune responses against the vector and the transgene (SIV-gag). In naive animals, cellular immune response was significantly higher by i.m. immunization; however, MV pre-immunity did not seem to affect the cellular immune response after Promazine hydrochloride an i.n. immunization. In summary, we show that a pre-existing immunity of up to 500 mIU anti-MV neutralizing antibodies had little effect on the replication of rMV and did not inhibit the induction of significant humoral and cellular immune responses in immune-competent mice. Keywords: vaccine, pre-existing immunity, immunization route, measles, SIV, recombinant virus, reverse genetics, immune competent mice Introduction Novel technologies in vaccinology are necessary to tackle today’s major diseases, such as AIDS, malaria and tuberculosis. Reverse genetics permits the designing of viruses, to be used as vectors, in order to deliver foreign antigens to the body.1-3 Due to its size, Measles virus (MV) is a an excellent vector candidate since its genome allows the incorporation of up to 40% of additional foreign nucleotides.4 The live MV vaccine has a long record of safety and efficacy, especially since the reversion to pathogenicity has never been observed with this vaccine. The live vaccine is injected subcutaneously or dispensed as an aerosol for adults, children and infants.2,10-12,22 Since the manufacturing and production of MV vaccine is well established, an MV-based vaccine vector would be easily manufactured and thus affordable. These characteristics prompted us and others to design and produce several MV vectors carrying diverse antigens derived from human pathogens, including Hepatitis B,5 Dengue,6 HIV-1,4,7,28 SARS8 and Malaria.9 For the rescue of recombinant measles viruses (rMV), a helper-cell based system had to be developed. The uniqueness of the rescue of these rMV viruses, using a human Rabbit Polyclonal to NOC3L cell line, represents an additional advantage in terms of vaccine safety. The measles vaccine has also been extensively used as an aerosol vaccine in children.2,9-12 Generally, aerosolized measles vaccine appeared to be more immunogenic than subcutaneous measles vaccines in children aged 10 mo and older. Aerosol applications Promazine hydrochloride have the advantage to be distributed over a significant surface, e.g., humans lungs represent around 50m2.1,2 In addition, the pulmonary, nasal and oral immune system comprise the mucosal-associated lymphoid tissues, which are responsible for the activation of approximately 80% of all immunocytes.13 Mucosal immunity is often the first line of defense against pathogens and is therefore of utmost importance. Many studies indicate that systemic immunization produce strong anti-viral systemic responses, while mucosal immunization can stimulate both the mucosal and systemic response and confer long-term immunological memory. However, the magnitude of these immune responses is often somewhat reduced, as seen with immunizations using adenovirus vectors.14-16,26 We constructed a MV-based vector containing various HIV-1 and SIV antigens with the ultimate goal of using it as pediatric vaccine against MV and HIV-1 infections. The possibility to dispense it as an aerosol is ideal for resource-limited countries where refrigeration and needle use are problematic. However, adults could also benefit of such an rMV-HIV-1 vaccine, since it could be used as an additional tool among HIV-1 therapeutics. Certain questions arose as to whether such a vaccine would still be efficacious in the presence of a MV pre-immunity, which can be expected in a large number of an adult population. As seen in the STEP and Phambili study, the presence of an anti-vector pre-immunity can have a detrimental impact on the development of an immune response and on the potential of a vaccine to protect against new infections.17-19 However, other studies showed that Ad5-based vaccines given by mucosal routes can Promazine hydrochloride circumvent the effect of pre-existing immunity and induce significant immune response against the.